A conventional technique of forming a laminate circuit board structures includes forming layers of dielectric material and electrically conducting material to provide multiple layers of circuits and voltage planes. Voltage planes can be either ground plane or power planes, and are sometimes collectively referred to as power planes.
Conventional printed circuit boards are typically constructed from glass cloth prepreg and copper. Normally copper clad laminates (CCL's) are circuitized and then “laid up” with other circuitized cores and additional sticker prepreg to form composites. Once laminated, conventional composite boards are drilled and then plated. While conventional boards can be either tri-plate or strip line constructions, both use conventional prepreg as sticker sheets. Both designs, especially stripline/buried via designs, also usually utilize signal to power plane referencing through the sticker sheet layer, on at least one side of the signal line.
Composites constructed using 2S1P building blocks offer a number of advantages over conventional construction techniques. One of these advantages is testable impedance prior to composite lamination. The impedance is also predominately controlled by the core dielectric. This is a major advantage as core layer dielectrics are not effected by the complex geometries and fill requirements that occur at composite lamination. 2S1P's built with glass cloth free materials facilitate very high circuit density by allowing very small, laser drilled holes to be made. One very important aspect of using 2S1P's to build high density composite printed circuit boards (PCBs) is the method used to adhere the 2S1P's into a composite board.
Prior methods of making 2S1P cores involve drilling or etching clearance holes in bare sheets, e.g., 2 oz., 1 oz. and/or 0.5 oz., copper and then laminating and fully curing these with conventional prepregs or coated foils to produce a core that could be circuitized forming the signal planes. Likewise, prior 0S1P's have been fabricated in similar manners. These methods are difficult to practice due to the problems associated with handling bare copper. 2S1P's can also be made by circuitizing one side of a core with the power pattern then relaminating additional prepreg or coated copper over the circuitized power pattern.
Regardless of the method used to make the 2S1P cores, they must now be stuck together using additional “sticker” materials placed between the 2S1P's and the 0S1P's. These additional sticker sheets contribute additional thickness and exacerbate all the problems associated with additional thickness.
More recently, techniques have been provided that provide a relatively inexpensive photolithographic technique of forming a composite laminate structure from individual discrete laminate structures into a composite laminate structure. Along these lines see U.S. application Ser. No. 09/203,945 entitled “Two Signal One Power Plane Circuit Board,” Ser. No. 09/203,978 entitled “Multi-Layer Organic Chip Carrier Package” and Ser. No. 09/204,458 entitled “Composite Laminate Circuit and Method of Forming the Same,” entire disclosures of which are incorporated herein by reference.
Although the structures and methods of these inventions provide significant advances and advantages over current printed wire board (PWB) fabrication methods, there still exists a need for further refinement. Therefore continuing efforts are underway in attempting to provide for even greater advantages.